Abstract Neutron diffraction is used to reveal the origin of the unusual thermal expansion properties of the itinerant-electron system Hf0.875Ta0.125Fe2. Hf0.875Ta0.125Fe2 shows temperature-induced magnetic transitions from ferromagnetic (FM) to antiferromagnetic (AFM) order and then to the paramagnetic (PM) state upon heating. The FM-AFM transition proceeds in a stepwise fashion, as a first-order phase transition, and is accompanied by an extremely anisotropic lattice collapse. The unit cell volume shrinks abruptly, but only in the basal plane; the dimension along the c-axis varies almost continuously. Hf0.875Ta0.125Fe2 exhibits a 0.37 % spontaneous volume contraction across the FM-AFM transition, where a giant negative thermal expansion (NTE), with a volumetric thermal expansion coefficient -74×10-6 K-1, is observed over a temperature interval of ΔT∼50 K around room temperature.

中文翻译：

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在 Hf0.875Ta0.125Fe2 中覆盖室温的磁驱动巨型负热膨胀

摘要 中子衍射用于揭示流动电子系统Hf0.875Ta0.125Fe2异常热膨胀特性的起源。Hf0.875Ta0.125Fe2 显示了在加热时从铁磁 (FM) 到反铁磁 (AFM) 顺序，然后到顺磁 (PM) 状态的温度诱导磁转变。FM-AFM 转变以逐步的方式进行，作为一级相变，并伴随着极其各向异性的晶格坍塌。晶胞体积突然缩小，但仅在基面；沿 c 轴的尺寸几乎连续变化。Hf0.875Ta0.125Fe2 在 FM-AFM 转变过程中表现出 0.37% 的自发体积收缩，其中巨大的负热膨胀 (NTE)，体积热膨胀系数为 -74×10-6 K-1，